Osteocalcin gives muscles an extra kick

Researchers have found the first bone-derived hormone known to affect exercise capacity

When we exercise our bones produce a hormone called osteocalcin that increases muscle performance.

It is not the only hormone responsible for adaptation to exercise in humans but it is the only bone-derived hormone that increases exercise capacity.

Osteocalcin makes up 1 to 2 percent of the bone’s mineralized matrix, though scientists found in previous studies the protein appears in the bloodstream and acts like a hormone in organs.

They also noticed the amount of osteocalcin in the bloodstream doubles during exercise — suggesting a greater role than previously understood.

According to Gerard Karsenty, a geneticist at the Columbia University Medical Center and senior author on the study published in the journal Cell Metabolism, it had never been shown before that bone actually influences muscle in any way.

“The hormone is powerful enough to reconstitute, in older animals, the muscle function of young animals,” Karsenty said.

Osteocalcin gives the muscles an extra kick by promoting fuel uptake and boosting the body’s ability to break down that fuel for energy use, making it easier to exercise longer and harder.

Levels of osteocalcin decline with age in humans, with the decline occurring about 15 to 20 years sooner in women than in men. “If you look backwards during evolution, men were much more active than women–for example, in hunting and fishing. That may be an explanation for why the decrease in circulating osteocalcin occurs later in men than in women,” said Karsenty.

Karsenty and colleagues measured the levels of glucose, glycogen as well as acylcarnitines, an indicator of fatty-acid use, in mice with and without osteocalcin and found that the hormone helped muscle fibers uptake and catabolize glucose and fatty acids as nutrients during exercise.

The research team observed that in 3-month-old adult mice, osteocalcin levels increased approximately four times the amount that the levels in 12-month-old mice did when the rodents ran for 40 minutes on a treadmill. To investigate whether osteocalcin levels were affecting exercise performance, the researchers tested mice genetically engineered so the hormone couldn’t signal properly in their muscles. Without osteocalcin muscle signaling, the mice ran 20% to 30% less time and distance than their healthy counterparts before reaching exhaustion.

Further research is needed to determine if injecting a bone hormone, that is produced during exercise, could help rejuvenating ageing muscles and increase the capacity of performing physical activities.